It is important that individual radiating elements in antenna arrays are closely spaced to prevent grating lobes in the antenna pattern. Ideally, the element spacing should be held to less than a half wavelength of the electro-magnetic (EM) wave in order to completely suppress these lobes, although in most cases slightly greater spacing is acceptable. Achieving this close spacing is difficult in waveguide feed systems where the waveguide has a minimum half wavelength width. In dual band antenna systems, the two feed systems must be designed to avoid mechanical interference with each other.
In the dual band waveguide systems, one band is typically brought in axially to the dual band radiating element while the other band is brought in from the side. The side-feed traditionally requires both an H-plane bend followed by an E-plane bend. The physical structure of H-plane bends and E-plane bends makes it is difficult to achieve close element spacing in dual band waveguide systems.